We observe hadronic W decays in ttbar -> W(-> l nu)+ \geq 4 jet
events using a 109 pb^-1 data sample of ppbar collisions at sqrt s = 1.8 TeV
collected with the Collider Detector at Fermilab (CDF).  A peak in the dijet
invariant mass distribution is obtained that is consistent with W decay and
inconsistent with the background prediction by 3.3 sigma.  From this peak we
measure the W mass to be 77.2 +/- 4.6 (stat+syst) GeV/c^2.  This result
demonstates the presence of two W bosons in ttbar candidates in the W(-> l
nu)+ \geq 4 jet channel.